Evolution of Spinal Endoscopic Surgery

Surgical therapy for spinal disease has been gradually changing from traditional open surgery to minimally invasive spinal surgery. Recently, endoscopic spinal surgery, which initially was limited to the treatment of soft tissue lesions, has expanded to include other aspects of spinal disease and excellent clinical outcome. With the increase in life expectancy, the number of patients with spinal disease is on rise and due to the increased patient age, surgeons now have to manage patients with increased medical comorbidities such as lung, heart and kidney dysfunction. Consequently, more spinal surgeries are being performed as minimally invasive spine surgery. Endoscopic surgery is a subset of minimally invasive spine surgery that has been evolving rapidly and continuously to help manage older and sicker patients. Endoscopic procedures have advantaged such minimal muscle and bone damage, less pain, early rehabilitation, reduced hospital stay and early return to work. Historically, the use of endoscopic spinal surgery was limited to discectomies but recently its indications have widened to include lumbar spinal stenosis and instabilities. With the enhancement of our understanding of pain generators of the spine and ever growing technological advancement, the horizon of spinal pathologies which can be managed endoscopically have expanded from degenerative to neoplastic, inflammatory, infective and other pathology. The application has crossed barriers of lesions of lumbar spine to cervical and thoracic pathologies.

BRIEF HISTORY OF ENDOSCOPIC SPINAL SURGERY

Endoscopic spinal surgery began as percutaneous endoscopic discectomy. Kambin (1973) and Hijikata et al. (1975) had attempted the earliest endoscopic surgery in 1970's. However, at that time, removal of lesion was not under direct visualization and therefore spinal canal decompression was indirect. Therefore, the technique of that time can be regarded as percutaneous endoscopic spinal procedure before percutaneous endoscopic spinal surgery. Later Kambin and colleagues introduced a method to remove nucleus pulposus using a 5-mm diameter working cannula and flexible forceps in 1986 and 1987. Subsequently, other authors reported improvement of percutaneous endoscopic discectomy techniques. In 1990, Kambin introduced the anatomical understanding of the transforaminal approach and triangular safe zone where a lesion can be approached without neural damage. This became a catalyst for endoscopic spinal surgery to develop rapidly with the use of slightly larger instruments and working channels.

GENERATION OF ENDOSCOPIC SPINAL SURGERY

The first generation of endoscopic spinal surgery can be epitomized by transforaminal endoscopic spine surgery. Yeung introduced minimally invasive disc surgery using the Yeung endoscopic spine system in 1999. This method substituted the already existing indirect percutaneous endoscopic procedure. As such, visualized endoscopic spine surgery began from this point. Percutaneous endoscopic lumbar discectomy was introduced in 1993. Afterwards, percutaneous endoscopic transforaminal discectomy approaching intervertebral foramen through posterolateral side of back was performed mainly as endoscopic spine surgery. The Yeung endoscopic spine system at this time was based on inside-out approach which had limited surgical indication. Epidural approach was attempted to address the limitations of the transforaminal approach that initially targeted the intradiscal space. Outside-in approach was first introduced by Schubert and Hoogland in transforaminal approach allowing wider range of transforaminal approach. The transforaminal approach became an epidural approach with direct access to most of the lesion sites through the half-and half approach, a transforaminal approach introduced in 2007. The transforaminal approach has 2 anatomical limitations. First, there are bony limitations including the facet joint in high canal compromise and pedicle in a highly inferiorly migrated disc. Second, there is the neurological limitation of exiting root. The exiting root include the dorsal root ganglion in relation with a foraminal disc. In later iterations of this technology, the bony limitations were overcome with introduction of endoscopic drills by Choi et al in 2008. Choi et al. presented exiting root injury in 2013, which was a step forward in endoscopic spinal surgery. Early endoscopic spinal surgery had limited surgical exposure and instruments. Kambin introduced the triangular safe zone however it had limitations due to neurological and anatomical barriers. There has been continuous evolution of the approach such as outside-in, inside-out and mobile outside-in techniques. Currently many of the earlier limitations of transforaminal endoscopic lumbar discectomy have been overcome. Recent studies have reported the clinical results of transforaminal endoscopy are as good as traditional open surgery.

SECOND GENERATION OF ENDOSCOPIC SPINAL SURGERY

Transforaminal endoscopic lumbar discectomy was developed as a common surgical treatment for disc herniations. However, inserting a cannula safely into the foramen at the L5-S1 level is difficult due to high iliac crest and narrow foramen. In addition, transforaminal endoscopic lumbar discectomy had longer surgery time and increased radiation exposure due to repetitive approach attempts. For this reason, the interlaminar approach was developed and introduced. As such, the second generation of endoscopic spine surgery can be epitomized by interlaminar endoscopic spine surgery. A discectomy performed through an interlaminar approach is referred to as interlaminar endoscopic lumbar discectomy. For this reason, interlaminar endoscopic lumbar discectomy was initially not included in the mainstream of endoscopic spine surgery and was an advanced form of microscopic lumbar discectomy. Interlaminar endoscopic lumbar discectomy was conducted in 2 main ways. They are the uniportal technique using one portal and the biportal technique using 2 ipsilateral portals.

THIRD GENERATION OF ENDOSCOPIC SPINAL SURGERY

The third generation is epitomized by endoscopic decompression, which refers to endoscopic lumbar decompression for stenosis. Previously spinal stenosis was a contraindication for endoscopic spine surgery. Now it has become an indication for endoscopic spine surgery due to rapid development in techniques and equipment. Endoscopic decompression requires less bone resection, muscle damage and can yield sufficient decompression despite the minimal neural retraction. Lumbar spinal stenosis is classified as central, lateral recess, or foraminal stenosis depending on the area of stenosis. General perception in endoscopic spinal surgery is that interlaminar approach is appropriate for central stenosis, both interlaminar and transforaminal approaches are appropriate for lateral recess stenosis, foraminal or extraforaminal stenosis. In addition to decompression of central and lateral recess stenosis by the interlaminar approach, decompression of foraminal or extraforaminal stenosis is now possible through foraminotomy. Lesions at multiple locations are more common in clinical practice and in such cases recently introduced percutaneous endoscopic contralateral interlaminar lumbar foraminotomy is highly effective.

NEWER INNOVATIONS OF ENDOSCOPIC SPINAL SURGERY

Maybe the fourth generation will be epitomized by lumbar interbody fusion, namely endoscopic lumbar interbody fusion. Supported by recent developments in surgical equipment, endoscopic spinal surgery can now be used for interbody fusion. However, fusion surgery using endoscope has still been associated with many complications such as subsidence and low fusion rate and has not been shown to have superior results compared to conventional fusion surgery. Nevertheless, attempts to solve these problems are continuing

FUTURE PERSPECTIVES

Historically, the drawbacks of endoscopic spinal surgery are incomplete surgery and dural tears. However, new innovations in endoscopic surgery have overcome the issue of incomplete surgery, and new methods of endoscopic dural repair have been reported. Recent reports show that endoscopic treatment is being extended to more advanced lesions such as intradural lesions. At the rate of current development, it is reasonable to predict that endoscopy will be an option to treat all spine disorders.

CONCLUSION

As described, endoscopic spinal surgery has many advantages and is rapidly replacing conventional spinal surgery. The next generation of endoscopic spinal surgery needs to be prepared to meet the needs of patients and show good clinical results in all areas of spinal disease.